Significance of ultrahigh-<i>P</i> talc-bearing eclogitic assemblages

Liou, J. G.; Zhang, R. Y.

doi:10.1180/minmag.1995.59.394.08

Cited by 31 publications

(12 citation statements)

References 15 publications

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“…The geological setting of the Dabie collision orogen has been studied by many authors (e.g., Hacker and Wang 1995;Liou and Zhang 1995;Suo et al 2000). The Bixiling Complex, the largest coesite-bearing mafi c-ultramafi c body (~1.5 km 2 ) in the Dabie Mountains, occurs as a tectonic block enclosed within quartzofeldspathic gneisses in the eastern part of the Dabie UHPM terrane.…”

Section: Geological Background Of the Bixiling Complexmentioning

confidence: 99%

Clinoenstatite exsolution in diopsidic augite of Dabieshan: Garnet peridotite from depth of 300 km

Liu

Zhang

Green

2007

American Mineralogist

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Clinoenstatite exsolution lamellae have been discovered in clinopyroxene grains of garnet peridotite from the Bixiling massif of the ultrahigh-pressure metamorphic (UHPM) terrane in the Dabie Mountains, China. Using transmission electron microscopy, we show here that although the lamellae are low clinoenstatite (Lclen) with P2 1 /c space-group symmetry, they contain nanometer-scale antiphase domains indicating that the originally precipitating phase had C2/c space-group symmetry. The lamellae are oriented parallel to [010] and ~18° to [001] of the host-approximately parallel to (401). Both the very cold exhumation path of the Dabie UHPM terrane and the orientation of the lamellae preclude the possibility that the originally precipitating phase could have been high-temperature clinoenstatite (HTclen). We conclude that the lamellae precipitated as high-pressure clinoenstatite (HPclen) and subsequently inverted to Lclen. Analysis of the incomplete high-pressure crystallographic data available for compositions approximating those of the lamellae and host suggests a minimum pressure of precipitation of ~9 GPa for Dabie and about 12 GPa for similar exsolution previously observed in the Alpe Arami peridotite, Switzerland. The Bixiling complex is a crustal cumulate, hence this result extends the minimum depth of subduction of continental rocks in the Dabie/SuLu orogen to ~300 km (P > 9 GPa).

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Section: Geological Background Of the Bixiling Complexmentioning

confidence: 99%

Clinoenstatite exsolution in diopsidic augite of Dabieshan: Garnet peridotite from depth of 300 km

Liu

Zhang

Green

2007

American Mineralogist

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“…As the largest ultrahigh-pressure (UHP) metamorphic terrain so far found worldwide, the Dabie-Sulu orogenic belt, which represents a Triassic collision zone between the North China Block and Yangtze Block, has attracted extensive interest from the geoscience community (Li et al, 1993(Li et al, , 1994(Li et al, , 2000Liou and Zhang, 1995;Zhang et al, 1995Zhang et al, , 2003Zhang et al, , 2005Carswell et al, 2000;Liou et al, 2000;Yang and Jahn, 2000;Sun et al, 2002). Research activities over the past decade have documented a number of characteristic features of this area, including rapid subduction to depths of greater than 100 km followed by rapid initial uplift (Xu et al, 1992;Li et al, 1993), the abundance of hydroxyl-bearing UHP mineral phases (Okay, 1995;Zhang et al, 1995), interaction between meteoric water and the rocks (Yui et al, 1995;Zheng et al, 1998), and variable fluid phases during UHP metamorphism (Xiao et al, 2000;Fu et al, 2001;Xiao et al, 2002).…”

Section: Geological Background and Samplesmentioning

confidence: 99%

Making continental crust through slab melting: Constraints from niobium–tantalum fractionation in UHP metamorphic rutile

Xiao

Sun

Hoefs

et al. 2006

Geochimica et Cosmochimica Acta

113

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“…Because of the coexistence of talc, amphibole and clinopyroxene as inclusions in grt p from foliated eclogites, two further water activity‐independent equilibria can be applied for geobarometry (Liou & Zhang, 1995; Massonne & Kopp, 2005) These barometers were combined with the talc‐garnet thermometer defined by equilibrium . The results are strongly dependent on the Al content in talc.…”

Section: Thermobarometrymentioning

confidence: 99%

A counter‐clockwise P–T path for the Voltri Massif eclogites (Ligurian Alps, Italy)

Vignaroli

Rossetti

Bouybaouène

et al. 2005

Journal Metamorphic Geology

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Integrated petrological and structural investigations of eclogites from the eclogite zone of the Voltri Massif (Ligurian Alps) have been used to reconstruct a complete Alpine P-T deformation path from burial by subduction to subsequent exhumation. The early metamorphic evolution of the eclogites has been unravelled by correlating garnet zonation trends with the chemical variations in inclusions found in the different garnet domains. Garnet in massive eclogites displays typical growth zoning, whereas garnet in foliated eclogites shows rim-ward resorption, likely related to re-equilibration during retrogressive evolution. Garnet inclusions are distinctly different from core to rim, consisting primarily of Ca-, Na/Ca-amphibole, epidote, paragonite and talc in garnet cores and of clinopyroxene ± talc in the outer garnet domains. Quantitative thermobarometry on the inclusion assemblages in the garnet cores defines an initial greenschist-to-amphibolite facies metamorphic stage (M1 stage) at c. 450-500°C and 5-8 kbar. Coexistence of omphacite + talc + katophorite inclusion assemblage in the outer garnet domains indicate c. 550°C and 20 kbar, conditions which were considered as minimum P-T estimates for the M2 eclogitic stage. The early phase of retrograde reactions is polyphase and equilibrated under epidote-blueschist facies (M3 stage), characterized by the development of composite reaction textures (garnet necklaces and fluid-assisted Na-amphibole-bearing symplectites) produced at the expense of the primary M2 garnet-clinopyroxene assemblage. The blueschist retrogression is contemporaneous with the development of a penetrative deformation (D3) that resulted in a non-coaxial fabric, with dominant topto-the-N sense of shear during rock exhumation. All of that is overprinted by a texturally late amphibolite/greenschist facies assemblages (M4 & M5 stages), which are not associated with a penetrative structural fabric. The combined P-T deformation data are consistent with an overall counter-clockwise path, from the greenschist/amphibolite, through the eclogite, the blueschist to the greenschist facies. These new results provide insights into the dynamic evolution of the Tertiary oceanic subduction processes leading to the building up of the Alpine orogen and the mechanisms involved in the exhumation of its high-pressure roots.

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Significance of ultrahigh-P talc-bearing eclogitic assemblages

Cited by 31 publications

References 15 publications

Clinoenstatite exsolution in diopsidic augite of Dabieshan: Garnet peridotite from depth of 300 km

Clinoenstatite exsolution in diopsidic augite of Dabieshan: Garnet peridotite from depth of 300 km

Making continental crust through slab melting: Constraints from niobium–tantalum fractionation in UHP metamorphic rutile

A counter‐clockwise P–T path for the Voltri Massif eclogites (Ligurian Alps, Italy)

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